The present invention relates to a run on prevention device for an internal combustion engine, one more particularly relates to a run on prevention device for an internal combustion engine which is provided with an exhaust gas recirculation system.
The problem of so called running on often arises with internal combustion engines. When it is desired no longer to operate such an engine the ignition circuit thereof, in the case of a spark ignition engine, is switched off, so that the engine should thereby stop rotating as soon as the rotational energy has been absorbed by friction. However, sometimes undesirably the engine continues to function in a so called dieseling mode wherein gasoline which is sucked into the combustion chambers in the normal way is ignited, not by any electric spark produced by the spark plugs, since the ignition system has been switched off, but instead by hot spots or the like within the combustion chambers, such as glowing morsels of carbon adhering to the sides thereof, especially around the exhaust ports and exhaust valves of the combustion chambers, which, when the maximum level of compression is attained during the compression stroke of a cylinder, are often able to ignite the fuel-air mixture. Thereby, the internal combustion engine may continue to rotate, since the carburetor thereof will continue to function irrespective of the on/off condition of the ignition circuit thereof.
Such running on is wasteful of fuel, and causes great unpredictability of the behavior of the internal combustion engine. Further, because as a matter of course such hot spot dieseling ignition is irregular, the rotation of the engine is irregular and imperfect, and accordingly a great deal of vibration and noise are produced during the running on condition, and this can be very annoying for the driver of a vehicle incorporating the engine, and for the occupants thereof. Further, because such compression or dieseling ignition, which operates by a mechanism similar to that of so called "pinking", often may well occur at a rather advanced point in the engine rotational timing chart, severe stress is often caused to the various mechanical components of such an engine which runs on, thus shortening their useful operating lives. Yet further, because as has been explained above the running on ignition during running on is imperfect and irregular, and may well only occur on a minority of the compression strokes of any particular combustion chamber, typically running on operation expels a great deal of unburnt fuel such as gasoline into the exhaust manifold of the engine. There is a possibility that this unburnt fuel may explode in the exhaust system, and this can be very troublesome, noisy, and dangerous. Further, the problem of overheating of a catalytic converter fitted to the exhaust system of the internal combustion engine, due to the feeding of large quantities of uncombusted hydrocarbons thereinto, is very serious.
This problem of running on has become more acute in modern automobiles in which measures for reduction of exhaust gas pollution have been incorporated. In such automobiles, typically spark timing is rather retarded, which promotes the accumulation of such carbon and soot deposits as provide good sites for the glowing parts or hot spots within the cylinder chamber which are involved in running on operation. Further, a large amount of valve timing overlap, and provision of exhaust gas recirculation, further contribute to the build up of these deposits. These operational parameters also contribute to hotter running of certain parts of the cylinder chambers of the internal combustion engine, which further encourages the production of these hot spots. Further, even a small amount of running on of an engine greatly increases the emissions of unburnt hydrocarbons in the exhaust gases thereof. Accordingly, in modern automobile engines, it has become necessary to take effective measures against such running on.
Several sorts of run on prevention systems have been previously proposed. A first way of preventing running on of an internal combustion engine has been to provide a fuel cut off mechanism in the carburetor, which interrupts the fuel supply passage within the carburetor in response to turning off of the ignition system of the engine by the ignition key thereof. This system works, but it has its drawbacks. Because within a modern carburetor there are several jets and orifices which supply fuel into the intake tract or throat thereof, since it is impracticable to provide separate fuel cut off mechanisms in all these passages, accordingly a fuel cut off mechanism must be provided at a position some way back in the direction of the flow of liquid fuel from the nozzles within the throat of the carburetor. Accordingly, when the engine is switched off, a certain amount of liquid fuel still remains between the fuel cut off mechanism and the ends of the nozzles within the carburetor throat, and accordingly the effect of this fuel cut off mechanism is not immediately obtained, and a certain amount of running on of the internal combustion engine is still able to occur. Further, the additional complication of the fuel passages within the carburetor may well deteriorate the accuracy of fuel metering by the carburetor, in some operational conditions of the internal combustion engine.
A second system that has been proposed and practiced for preventing running on of an internal combustion engine has been to provide a special air supply valve which, when the engine is switched off, opens so as to provide a large amount of air directly into the intake system of the internal combustion engine, bypassing the carburetor. Thereby, a large amount of excess air is provided to the air-fuel mixture that is being sucked in by the internal combustion engine for dieseling operation, and accordingly it is hoped that dieseling ignition of this very weak air mixture by hot spots and the like will be prevented. However, there are problems with this approach. First, it is quite possible that the internal combustion engine may be able to operate in the over lean mode, and to ignite such over lean air-fuel mixture, in which case this system will be ineffective. Further, the provision of such a relatively large air supply valve, and large diameter air pipes leading to and from it, is troublesome and expensive, and is inconvenient for design of the intake system of the internal combustion engine, and for location thereof within the engine compartment. Further, problems arise such as possible changes in the air/fuel ratio when the internal combustion engine is operating in the normal operational mode, due to possible leakage of such an air supply valve, which, even in a small amount, can greatly deteriorate the operability of the engine. Yet further, due to the fact that the air intake system of an engine including such an air supply valve is of large diameter and accordingly of a very low air flow resistance, difficulties arise with regard to the restartability of the engine, especially from the cold condition.
Accordingly, as yet no fully suitable and operable run on prevention system for an internal combustion engine has been proposed.
In modern engines, as mentioned above, the problem of reducing the amount of noxious pollutants in the exhaust gases is severe. One of the conventional solutions for reduction of the level of pollutants in exhaust gases is to provide exhaust gas recirculation for the internal combustion engine, wherein an exhaust gas recirculation conduit is provided which connects a part of the exhaust system of the engine to a part of the intake manifold thereof after the carburetor, so that a certain amount of the exhaust gases which are being blown out through the exhaust system is instead taken into this exhaust gas recirculation passage, and is recycled into the inlet manifold. Within the exhaust gas recirculation passage there is typically provided an exhaust gas recirculation control valve, and this again typically is controlled by supply of actuating vacuum thereto, and in response to such supply of actuating vacuum opens and closes a valve port by a valve element, so as to vary the effective flow resistance of the exhaust gas recirculation conduit and so as to provide a proper amount of exhaust gas recirculation according to the current operational conditions of the internal combustion engine. Further, in certain systems, it is well known and conventional for the actuating vacuum which actuates this exhaust gas recirculation control valve to be provided from a vacuum take off port situated within the throat of the carburetor at a position which is upstream of a butterfly throttle valve thereof when the throttle valve is fully closed, but which is downstream of said throttle valve when said throttle valve is opened by more than a certain predetermined small amount.
Such an exhaust gas recirculation control system has been found effective in practice for reducing the amount of undesirable noxious pollutants in the exhaust gases of an internal combustion engine. Further, as a refinement thereof, it has been practiced to provide a pressure plenum within the exhaust gas recirculation passage, just upstream of the valve port and the valve element of the exhaust gas recirculation control valve, the pressure within which controls a vacuum adjustment valve which modifies said vacuum produced by said vacuum take out port within the throat of the carburetor in such a way that the exhaust gas recirculation control valve is controlled in its opening and closing amount in such a way as to maintain the pressure within said pressure plenum effectively constant. This ensures that the amount of exhaust gas which is recirculated to the exhaust gas recirculation passage is proportional to, i.e., is linearly dependent upon, the total amount of the gases which are being inhaled by the internal combustion engine through the inlet manifold thereof. In other words, such an arrangement ensures a substantially constant exhaust gas recirculation ratio, substantially irrespective of the opening of the intake throttle valve of the internal combustion engine, and of the revolution speed thereof.